1. Field of the Invention
The invention relates to a method and apparatus for verifying the position of a lesion to be treated by a radiation therapy device operating in accordance with a radiation therapy plan.
2. Description of the Prior Art
Modern day radiation therapy of cancerous tumors, or lesions, has two goals: eradication of the tumor and avoidance of damage to healthy tissue and organs present near the tumor. It is believed that a vast majority of tumors can be eradicated completely if a sufficient radiation dose is delivered to the tumor volume; however, complications may result from use of the necessary effective radiation dose, due to damage to healthy tissue which surrounds the tumor, or to other healthy body organs located close to the tumor. The goal of conformal radiation therapy is to confine the delivered radiation dose to only the tumor volume defined by the outer surface of the tumor, while minimizing the dose of radiation to surrounding healthy tissue or adjacent healthy organs.
Conformal radiation therapy treatment typically uses a linear accelerator as a source of the radiation being used to treat the tumor. The linear accelerator typically has a radiation beam source which is rotated about the patient and directs the radiation beam toward the tumor, or lesion, to be treated. Various types of devices have been proposed to conform the shape of the radiation treatment beam to follow the spatial contour of the tumor as seen by the radiation treatment beam as it passes through the patient's body into the tumor, during rotation of the radiation beam source, which is mounted on a rotatable gantry of the linear accelerator. Multileaf collimators, which have multiple leaf, or finger, projections which can be moved individually into and out of the path of the radiation beam, can be so programmed, and are examples of such devices. Various types of radiation treatment planning systems can create a radiation treatment plan, which when implemented will deliver a specified dose of radiation shaped to conform to the lesion, or tumor, volume, while limiting the radiation dose delivered to sensitive surrounding healthy tissue or adjacent healthy organs.
A basic problem in radiation therapy is knowing where the target, or lesion or tumor, is located at the time the radiation therapy treatment is occurring. It is assumed that the patient's position and the target organ's position within the patient will be grossly the same at the time of radiation treatment, as it was at the time the radiation treatment plan was created. If the position of the target organ, or lesion or tumor, is not the same as it was at the time the treatment plan was determined, the conformal dose of radiation may not be delivered to the correct location within the patient's body. Since patients are not always positioned properly on the treatment table of the radiation therapy device, which is typically a linear accelerator, and since organs of a patient may move within the patient from day to day, the target organ, or lesion or tumor, may not be positioned at the exact location where the radiation therapy plan has assumed it would be located. Thus, present day radiation therapy plans typically regard the target organ to occupy a space in the patient's body which is larger than it really occupies, in order to insure that the target organ, or tumor or lesion, regardless of its location within the patient's body, falls within the volume of tissue which receives the desired radiation treatment dose. A disadvantage of such conventional radiation therapy plans is that there is a major concern associated with increasing the volume of tissue which is treated, to insure that the actual target organ receives the desired dose of radiation. Because some healthy tissue surrounds the target organ, or healthy organs lie adjacent to the target organ, delivering the maximum desired radiation dose to this larger volume of tissue may occur and increase risk of damaging such non-target tissue, or surrounding healthy tissue or adjacent healthy organs. This increased risk may cause oncologists to deliver a radiation dose to the larger treatment volume, which is safer for the non-target tissue, with the potential disadvantage of underdosing some portion of the target organ.
Accordingly, prior to the development of the present invention, there has been no lesion position verification system or method for verifying the position of a lesion within a body of a patient for use in a radiation treatment plan, which: regardless of the position of the patient on the treatment table, can verify that the position of the lesion to be treated conforms to the position of the lesion utilized in the radiation treatment plan; and prevents treating healthy tissue surrounding the lesion, or healthy organs located adjacent the lesion, from being exposed to an undesired level of radiation.
Therefore, the art has sought a method and apparatus for verifying the position of a lesion, within a body of a patient for use in a radiation treatment plan, which: verifies that the position of the lesion to be treated by the radiation therapy device is positioned to conform to the position of the lesion used in the radiation treatment plan; and prevents healthy tissue surrounding the lesion, or healthy organs located adjacent the lesion, from being exposed to an undesired amount of radiation.